Great question. You don't actually state it so I have to ask: by specifying "Protestant" ceremonies, is the comparison to Eastern Orthodoxy (EO)? If so, then why isn't the comparison the original Christian practice that preceded the great schism? If I go a step further, why isn't this inquiry couched in the Judaic practices and the messianic foreshadowing of those rituals found in the Old Testament? Why measure Protestantism by a set of conditions that did not exist for the first thousand years in Christendom?
I understand this is the EO board. I have nothing against EOism, so I would like you to know this is post not a troll. I assume you're familiar with the history of the Orthodox Church and, therefore, already know the EO is itself a an institution (church, denomination, or sect if you prefer) that has its origins in protest. It, therefore, would be correct and just to call the Orthodox protestant (small "p"). Similarly, the Protestant Church was formed from an effort to restore orthodoxy (small "o") to Christian thought, doctrine, and practice. Each institution was simply focusing on problems in the Roman Catholic Church that existed at the respective times of each groups beginning. More importantly, not only were both groups "birthed" as a consequence of protest, and protest against political and doctrinal error, but both also have their roots in Judaism - especially the rituals of baptism (and other conversion-related rituals) and marriage. Doctrinally speaking (Christologically, soteriologically, ecclesiologically, and eschatologically) we (EOs and Prots) also share a lot of common ground regardng those two rituals and their accompanying theologies.
So, if you wouldn't mind, aside from the presumption you're EO, why couch these inquiries in Orthodoxy as the measure instead of some of the common ground measures?
As a Protestant of no particular denominational allegiance (I do not believe God is a respecter of denominations or denominationalism) I'll offer an answer to your inquires. The first is logistical. Suppose the Orthodox Church rejected the baptisms and marriages of converts. The necessary implication would be that those converts were never married. We might qualify that as "never correctly married," but that only obfuscates the underlying point. If their marriage was false then their marriage begins only once the EO ceremony is performed. Can you see how that would be a practical problem? Another approach is couched in the fact Jesus accepted, affirmed, and asserted marriage in Judaism, and not once did he state, or remotely imply, a Jewish wedding was invalid (in fact, I do not recall him ever implicating a Gentile marriage, either). Therefore, formerly Jewish converts who are married in Judaism would, in theory, have a more historic practice in their ceremony than the EO. There is, potentially, a simple solution: a renewal of vows. My second avenue for answering the op's inquiries is more doctrinal. Because Christian marriage is understood to have relevancy to the doctrines I listed above (marriage is Christological, soteriological, eschatological, etc.) and we all share a lot of common ground there, it becomes incumbent upon the EO to specify the points of departure relevant to each doctrine. I can't see that any of those differences is going to have a practical distinction. Jewish, Orthodox, and Protestant marriage is still a ritual or ceremony first seeded in Genesis (Adam and Eve), and marriages is still a ceremony foreshadowing the Lamb's marriage feast.
So perhaps you could specify what you think are salient concerns predicated on actual differences between Orthos and Prots. Take your time. I've got to go soon and may not be back in the forum today.